Automotive radiators and other heat exchangers have a series of parallel flat tubes carrying a hot fluid such as engine coolant for transfer of heat to a cooler fluid such as air which flows around the tubes. To improve heat transfer rate, sinuous or corrugated metal strips called fins or air centers are inserted in the spaces between the flat tubes and soldered or brazed at the junction of the peaks of the air centers and the tubes to assure good heat conductivity from the tubes to the fins. The tubes are assembled in the radiator at fixed spacings and the air centers then must be just the right size to fit in the spacing. Different products may have different heat transfer requirements and thus require centers with different fin spacings.
A prior practice used for obtaining centers of different fin spacings from a machine which has forming rolls for producing a set number of corrugation peaks or convolutions per unit length of strip stock is to change the tooling. A conventional way of controlling the pitch is to stuff or pack the centers such that the convolutions are touching and then stretching out the centers by pullout rolls until the desired pitch is obtained. To vary the pitch a pair of pullout rolls are removed from the machine and a different set of pullout rolls with a different number of teeth are substituted. This requires considerably machine downtime for the change-over as well as labor cost.